The analysis of ion(s) present in water at concentrations below the 100 ppb level is generally inaccurate and/or difficult. This analysis problem is compounded when other ions are present in the same solution at much greater concentrations. Previously, we have submitted patent applications J. S. Bradshaw, R. M. Izatt and J. J. Christensen, PROTON IONIZABLE MACROCYCLIC COMPOUNDS AND SELECTIVE COMPETITIVE SEPARATION OF DESIRABLE METAL IONS FROM MIXTURES THEREOF WITH OTHER IONS, U.S. patent application Ser. No. 07/036,664 filed Apr. 8, 1987 as continuation-in-part of U.S. patent application, Ser. No. 06/859,308 filed May 5, 1986; and J. S. Bradshaw, R. M. Izatt, J. J. Christensen, and R. L. Bruening, MACROCYCLIC LIGANDS BONDED TO SILICA AND THEIR USE IN SELECTIVELY AND QUANTITATIVELY REMOVING AND CONCENTRATING IONS PRESENT AT LOW CONCENTRATIONS FROM MIXTURES THEREOF WITH OTHER IONS, U.S. patent application, Ser. No. 07/240,689 , filed 09/06/88, which disclosed the bonding of macrocycles, which do not contain electron withdrawing groups, to silica via a side chain which is not connected to one of the electron rich macrocycle donor atoms (the compounds of FIG. 1). These bonded macrocycles have been shown to selectively form strong bonds with particular ions or groups of ions similar to the behavior of the same macrocycles present as solutes in solution. We have also discovered in our research that plain silica gel selectively binds certain cations present as solutes in solution. Prior researchers who have studied the analytical applications of silica gel and macrocycle-bonded silicas have confined their investigations to chromatographic applications where ions are present in concentrations greater than the ppb range. The concentration and subsequent analysis of selected ions requires quantitative and selective complexation of the ions so that the ions may be sufficiently concentrated. The extent of macrocycle-ion or silica gel-cation interaction is particularly important when ions present in solution at low concentrations need to be complexed. The greater the value of the equilibrium constant for ion-macrocycle or cationsilica gel interaction, the lower the initial concentration of the ion in solution can be and still be efficiently and quantitatively complexed, and therefore removed from the solution. Silica gel forms strong bonds with only a few selected cations. However, various macrocycles form strong and selective bonds with numerous ions, when the macrocycles are present as solutes in solution. An extensive compilation of the association constants between macrocycles and various cations is found in an article by R. M. Izatt, J. S. Bradshaw, S. A. Nielsen, J. D. Lamb, J. J. Christensen, and D. Sen, THERMODYNAMIC AND KINETIC DATA FOR CATION-MACROCYCLE INTERACTION, Chem. Rev., 1985, Vol. 23, 271-339. The ability to attach these macrocycles to silica without reducing the ability of the macrocycle to complex ions is of the utmost importance in their use as a concentrator for analytical purposes. In this patent we report the successful use of bonded macrocycles and in certain instances plain silica gel for this purpose.